Automatic hydraulic selector-operating mechanism for change speed gears



July 31, 1956 D P. HARRIS 2,756,611

AUTOMATIC HYDRAULIC SELECTOR-OPERATING MECHANISM FOR CHANGE SPEED GEARS Filed Dec.- 11, 1955 FIG.-

22 MM/7 IUUQ'UUUUQ I United States. Patent AUTOMATIC HYDRAULIC SELECTOR-OPER- MECHANISM FOR CHANGE SPEED David P. Harris, Moseley, Birmingham, England, assignor to The Austin Motor Company Limited, Birmingham, England Application December 11, 1953, Serial No. 397,704

Claims priority, application Great Britain December 18, 1952 6 Claims. (Cl. 74472) This invention relates to change speed gears and has for its object to provide a new or improved automatic hydraulic selector-operating mechanism therefor. More particularly the invention has for its object to provide an automatic hydraulic selector-operating mechanism for use in a gear-change system in which clutch and gear-shift operations are effected automatically and in correct sequence by actuation of a selector, e. g. a valve, or equivalent selector element.

According to the present invention, an automatic hydraulic selector-operating mechanism comprises a positive displacement pump the output of which is propor tional to gear-box output speed, a pressure responsive element, for operative connection to a gear selector, which element at all times is subjected on one side directly to pump output so as to be moved by variations therein, a restricted exhaust means for the pressure responsive element, and means whereby the eflective restriction of said exhaust means is varied at predetermined positions in the range of movement of the pressure responsive element, so that such movement is periodically arrested and consequently step-by-step movement is imparted to the gear selector.

The invention is particularly applicable to automobiles, and in any such application it is desirable that the vehicle speed at which each gear change is made should be capable of some modification by the degree of throttle opening. In this connection and according to a further feature of the invention, movement of the pressure responsive element is modified by an auxiliary control which is brought into operation when an engine throttle pedal is depressed. Such control preferably comprises either a secondary pressure responsive element which is subjected to engine inlet manifold pressure, or a mechanical connection between the pressure responsive element and the engine throttle pedal, which connection incorporates a yieldable member such as a spring.

Preferably the first pressure responsive element comprises a hydraulic cylinder and piston, the working space of the cylinder at one side of the piston being in direct communication with pump output so that the piston is subjected on that side to the pressure prevailing in front of the restricted by-pass, movement of the piston under the prevailing pressure being opposed by spring-loading, and the exhaust means comprising a number of flow branches, each of which affordsa restriction and connects with the cylinder at appropriately spaced points along its length, the pump output being connected directly to the working space of the cylinder in front of the restriction in the first flow branch of the exhaust means and the arrangement being such that the remaining flow branches are in turn opened to the cylinder working space by the piston as it is moved by increases in pump output.

In this way the effective restriction of the exhaust means is reduced with the introduction of each branch in turn, and each such introduction arrests the movement of the 2,756,611 Patented July 31, 1956 "ice piston until such time as pump output exceeds the increased exhaust means capacity.

Means may be provided whereby the restriction of the first flow branch of the exhaust means is variable'in inverse proportion to temperature so as to provide that the pump speeds at which gear changes are efiected remain substantially constant irrespective of changes in viscosity in the working fluid.

In the accompanying drawings the present invention is illustrated diagrammatically as applied to an automobile change-speed gear in which clutch and gear-change operations are effected automatically and in correct sequence by actuation of a selector in the form of a valve, Fig. 1 being a plan view and Fig. 2 being a fragmentary side elevation of part of Fig. 1.

Fig. 3 is a similar view to Fig. 1, showing an alternative arrangement.

Referring to Figs. 1 and 2 of the said drawings, the pump 10 is driven, for example, from the gear-box output shaft, so that pump output is directly proportional to vehicle speed. A first flow branch 11 connects pump output directly to the working space of a hydraulic cylinder 12 and to one side of a single-acting piston 13 therein, said piston 13-being'subjected to the pressure prevailing in front of a first restriction 14 in the flow branch 11, past which restriction 14 the working fluid can by-pass the cylinder 12 and return to the pump inlet side via the conduit 15.

Said conduit 15 is connected by a pipe line 16 to the other side of the piston 13, so that the piston 13 is subjected initially to the pressure prevailing upstream and downstream of the restriction 14, and movement of the piston due to pressure in the working space of the cylinder 12 is opposed by a spring 17.

The body of the cylinder 12 is connected, at spaced points along its length, with the return conduit 15 by means of three further flow branches 18, 19 and 20 respectively, each of which is restricted at 21.

The rod 22 of the piston 13 is arranged to rotate a pinion 23 as it is moved in its cylinder 12, and rotation of said pinion 23 effects rotation of a cam 24 which in turn operates a push rod 25. The latter effects appropriate actuation of a selector in the form of a valve 26, the

functionof which has been defined above.

In addition, rotation of the pinion 23 also operates a further cam 27, which in turn actuates a further push rod 28 which operates a gear-box cross-shift mechanism, of conventional form, indicated generally by the reference numeral 29 in Fig. 1, and which determines in respect of which of two pairs of gears the double-acting selector valve 26 shall operate.

In the diagrams the positions of the various moving parts are consistent with first gear being already engaged, the selection of first gear in starting from rest being effected manually.

As vehicle speed increases, the pump discharge increases proportionally, and rapidly increasing pressure in front of the restriction 14 of the by-pass acts upon the right hand side of the piston 13 in the working space 12, and moves the piston to the left until the flow branch 18 commences to be opened to the Working space 12. The pressure in the working space 12 now increases only very slowly in proportion to increasing vehicle speed until the branch 18 is fully open to the working space, because the effective restriction of the exhaust means afforded by the first flow branch has been reduced by the addition of the restricted branch 18 to the exhaust means.

Thus it will be seen that movement of the. piston 13 is arrested and such arrest is arranged to effect a pause in piston movement, the piston 13 functioning in the manner of a relief valve. When the flow branch 18 is fully open, the pressure moving the piston 13 again increases afforded by a side face of the same rotor body 32.

with the square of the pump speed, the piston moves rapidly to the left, the cam'24 is rotated and the selector valve 26 is moved to bringabout a change of gear from first to secondgear.

As flow "branches 19 and 20 respectively are reached a similar arrest of piston movement and a pause occur 'beforethe next gear is selected.

Gears .3 and 4, of course, entail an operation of the cross-shift mechanism 29 from the cam 27. Each of the four possible positions of the cam 24, corresponding to engagement of one of four forward gears, is detent indexed by the spring-loaded 'ball 30 (Fig. 2) engaging in sockets 31 in a cylinder rotor body 32 with which the cam 24 rotates, the profile of the cam 27 being shown as In this way, each position of the selector actuating cam 24 is indexed by a spring detent so that the said selector cam and selector valve 26 move quickly once the springloading is overcome.

Means for effecting a change-over to manual operation may be incorporated, and such means are indicated in Fig. l of the drawings, in which the pinion 23 is freely mounted on its shaft and a sliding dog 24* (shown disengaged) establishes or breaks driving connection between thepinion 23 and the cam 24. The arrangement will be such that this manual override, in disengaging the pinion v23 from the cam 24, allows the latter to be rotated independently of the pinion and associated mechanism.

Provision is made so that the vehicle speed at which each gear change is made is modified when variations of throttle opening occur, and one such arrangement is indicated in Fig. l which shows, diagrammatically, the piston rod 22 connected to a pressure responsive diaphragm 33*,

'one side of which is subjected to suction of the engine inlet manifold through conduit 34. The arrangement is such that at low throttle openings the increased suction (i. e. drop in pressure) in the inlet manifold assists movement of the piston 13.

tion to the type of gear box in which the bottom gear has no synchronising device, and, as hereafter described,

.automatic changes down into bottom gear are prevented.

The piston 33 has a central bore 34, with valve seats '35, 36 at the respective ends, and the piston rod 37 extends slidably into said bore 34, the portion 38 of the rod within said bore being formed with valve surfaces 39, 40 at its ends, which mate respectively with the valve seats 35, 36. Thus fluid has access to the bore 34 of the piston from one end or the other according to whether the piston 33 is being moved to the left by pressure fluid, or to the right by the spring 17.

A restrictor valve is shown at 42, and is normally closed.

On starting from rest, first gear is selected manually, as in the previous embodiment, and as the speed of the pump increases the piston 33 is moved to the left by pressure fluid until the first parallel flow line 43 commences to open to a passage 44 in the body of the piston. The valve surface 40 is engaging the valve seat 36 so that the right hand end of the piston bore 34 is closed. Move ment of the piston 33 is virtually arrested until the line 43 is fully open. Further increase in pump delivery eventually causes thepiston body to cover the flow line 43, and since the discharge of the pump is then effective upon the piston it must move instantly to open the further parallel jflow'line 45 to the passage 44 where it again pauses, this movement corresponding to engagement of second gear. Similarly the piston 33 moves to flow lines 46 and 47 to effect further gear changes in the upward sequence.

With the passage 44 aligned with the flow line 47, corresponding to engagement of fourth gear, as the pump speed decreases the spring 17 moves the piston 33 to the right. The right hand end of the piston bore 34 is opened to pump delivery, as the valve face 39 engages the valve seat 35 at the left hand end of said bore 34, so that pump delivery now has access to the piston bore, and from the bore 34 it passes to an exhaust line 48 through one of two lateral passages 49 in the piston body, so allowing the piston to move to the right until the flow line 46 is uncovered to the passage 44 in the piston. Simultaneously with the uncovering of the flow line 46, the exhaust line 48 is covered by the land 50 on the piston body and the piston pauses. Thus there is no opposition by pressure fluid to movement of the piston to the right, except when the passage 44 in the piston aligns with one of the two parallel flow lines 46 and 45, during its return movement, and the exhaust line 48 is closed by the piston body.

Consequently return movement of the piston 33 is also intermittent, and the rate of movement of the piston to select lower gears in the downward sequence does not depend upon the rate of decrease of pump speed.

When the piston has returned as far as to align the passage 44 with the flow line 45 no further return movement can occur, because this would shut off all flow from the pump. Therefore bottom gear cannot be engaged until the valve 42 is opened manually, which would only be done when the vehicle is stopped, in order to restart.

The alternative means of altering, at different throttle openings, the speeds at which gear changes occur, is indicated diagrammatically at the right hand side of Fig. 3, in which the piston 33 is shown as having an extension 51 acted upon by a spring 52 tending to oppose movement of the piston 33 to the left, i. e. to effect upward gear changes. The pivotal lever 53 rocks through link 55 according to the movement of pedal 54, which also operates engine throttle 56 through links 57 and 58 so as to vary the loading force of the spring 52, according to throttle actuating lever movements, say by mechanical connection therewith, so as to vary the loading force of the spring 52, the effect being to tend to delay engagement of a higher gear if the throttle is opened in one of the lower gears, and also to assist piston movement to the right, from a higher gear to a lower, upon such throttle openings.

The automatic hydraulic selector-opening mechanism according to this invention is suitable for use as a unit in converting existing semi-automatic gear change mechanisms, incorporating a selector as herein previously defined, for fully automatic operation, in addition to its obvious use as a sub-unit in fully automatic gear change systems.

Having fully described my invention, what I claim and desire to secure by Letters Patent is:

1. An automatic hydraulic gear selector operating mechanism for shiftable change speed gears of the type utilized to transmit motion of an engine-operated drive member to a driven member with the speed ratio of said members being dependent upon the gearing arrangement of said shiftable gears, said arrangement being determined through the positioning of a gear selector, said mechanism comprising: a positive displacement pump operatively connected to said driven member for delivering fluid to the output of said pump in proportion to the speed of said driven member, a working chamber connected to the output of said pump, a movable fluid pressure responsive element in said working chamber operatively connected to said selector and having a pressure receiving side subjected at all times to fluid output of said pump, yieldable means opposing movement of said element, fluid exhaust means connected to said working chamber and adapted to be opened to the receiving side of said element upon movement of said element to a predetermined position in its range of movement, fluid restricting means in said fluid exhaust means, means for periodically and progressively decreasing the effective area of the fluid restricting means at successive predetermined points in the range of movement of said element whereby upon any periodic decrease in the eflective area of said restricting means the pressure acting on said element is momentarily relieved and a step-by-step movement is imparted to said element and the selector connected thereto.

2. An automatic hydraulic gear-selector operating mechanism in accordance with claim 1 including in addition means for controlling said engine-operated drive member including a depressible engine throttle control pedal, and auxiliary control means for said pressure responsive element comprising means responsive to the depression of said pedal and operatively connected to said element for modifying movement thereof upon depression of said pedal.

3. An automatic hydraulic gear-selector operating mechanism in accordance with claim 1 including in addition means for controlling said engine-operated drive member including an internal combustion engine having an inlet manifold and a depressible engine throttle control pedal Whose degree of depression determines the pressure in said inlet manifold, a second fluid pressure responsive element subjected to engine inlet manifold pressure, and means operatively connecting said first fluid pressure responsive element with said second pressure responsive element to modify the movement of said first element in accordance with the depression of said engine throttle control pedal.

4. An automatic hydraulic gear-selector operating mechanism in accordance with claim 1 including in addition means for controlling said engine-operated drive member including a depressible engine throttle control pedal, and a yieldable mechanical connection between said pressure responsive element and said pedal for modifying movement of said element in accordance with the degree of depression of said pedal.

5. An automatic hydraulic gear selector operating mechanism for shiftable change speed gears of the type utilized to transmit motion of an engine-operated drive member to a driven member with the speed ratio of said members being dependent upon the gearing arrangement of said shiftable gears, said arrangement being determined through the positioning of a gear selector, said mechanism comprising: a positive displacement fluid pump operatively connected to said driven member for delivering fluid at the output of said pump in proportion to the speed of the driven member, a hydraulic cylinder, a piston in said cylinder forming therewith an expansible Working chamber, means directly connecting said chamher with the output of said pump, fluid exhaust means communicating with said cylinder and having fluid restricting means therein, spring means Opposing movement of said piston under the prevailing pressure, said exhaust means comprising a plurality of flow branches each containing a restriction and connected with said cylinder at spaced intervals along its length, said flow branches being in turn opened to the cylinder working chamber by said piston as it is moved by increases in pump output whereby movement of the piston takes place step-by-step, and a piston rod operatively connecting said piston with said gear selector.

6. An automatic hydraulic gear selector operating mechanism according to claim 5 wherein said piston is movable to a bottom gear position at the fluid receiving end of said working chamber means being provided for controlling the movement of said piston into the bottom gear position, said means comprising: a fluid passage in said piston connecting said chamber with the periphery of said piston to afford a fluid connection between said chamber and the flow branches of said exhaust means, a bypass conduit adjacent the outlet of said pump, a restrictor valve in said bypass which when opened directly bypasses pump output to exhaust to enable said piston under the action of said spring to move into bottom gear position, and when said valve is closed and at low pump output ensures that movement of said piston under the action of said spring means terminates at the first flow branch of the exhaust means whereby movement of said piston into bottom gear position is prevented.

References Cited in the file of this patent UNITED STATES PATENTS 941,426 Loudon Nov. 30, 1909 1,199,640 Vincent Sept. 26, 1916 2,590,232 Chilton Mar. 25, 1952 2,599,214 Wemp June 3, 1952 2,604,197 Livermore July 22, 1952 2,606,456 Dodge Aug. 12, 1952 2,633,035 Livermore Mar. 31, 1953 2,640,372 Dodge June 2, 1953 

